1. Field of the Invention
This invention relates to an intake system for a V-type engine, and more particularly to an intake system for a V-type engine which is arranged for supercharing by the kinetic effect of intake air.
2. Description of the Prior Art
Various multiple-cylinder engines are known which are arranged to increase the volumetric efficiency, and thereby the engine output torque, by the kinetic effect of intake air. For example, in the multiple-cylinder engine disclosed in Japanese Pat. Publication No. 60(1985)-14169, the cylinders are divided into first and second cylinder groups so that the cylinders in each cylinder group do not fire one after another, and the cylinders in the first and second cylinder groups are respectively connected to first and second intake passages, each of which comprises an enlarged volume chamber to which discrete intake passages are connected at the upstream side ends, and a resonance intake passage connected to the enlarged volume chamber. The upstream end of each resonance intake passage is communicated with an upstream side junction, and the enlarged volume chamber is provided with a switching means for selectively bringing the first and second intake passages into communication with each other or interrupting communication therebetween. When communication between the first and second intake passages is interrupted, negative pressure waves generated by the intake strokes in each cylinder are reflected at the upstream side junction as positive pressure waves, and an inertia supercharging effect is obtained by the positive pressure waves at relatively low engine speed ranges. On the other hand, when the first and second intake passages are communicated with each other, the negative pressures are reflected nearer the intake port than when communication between the intake passages is interrupted, whereby the natural frequency of the intake pressure oscillation is increased, and an inertia supercharging effect is obtained at higher engine speed ranges.
Further, supercharging can be effected by a resonance tuning effect by connecting the cylinders in each cylinder group (the cylinders which do not fire one after another) to an intake passage which has having no enlarged volume chamber, like a surge tank, and by selecting the length of the intake passage so that the resonant frequency of the intake air in the intake passage conforms to a particular engine speed range.
Based on the concepts used in such conventional intake systems, it would be expected to supercharge a V-type engine by the resonance effect of intake air by arranging the firing order so that the cylinders in each cylinder bank do not fire one after another, by communicating the cylinders in each cylinder bank by way of a resonance communicating passage and by connecting the resonance communicating passages for the respective cylinder banks to an intake air supply passage so that intake air resonates in the resonance communicating passages and the intake air supply passage.
The frequency of oscillation of the intake air depends upon the effective length of the intake passage. In order to obtain a sufficient supercharging effect by the kinetic effect of the intake air at low engine speed ranges, the intake passage must be long. However, the size of the intake system of an engine carried by a vehicle is naturally limited by the space allotted to the engine.